This invention relates to a method for analysing the driving behaviour of motor vehicles.
Target variables in developing and optimizing the power system of motor vehicles are emission behaviour, fuel consumption, performance and driveability. In general, driveability is a subjective concept, in particular concerning the behaviour of a vehicle in transient operational states as assessed by the driver. When the accelerator pedal of a car is depressed rapidly the driver will feel more comfortable if acceleration sets in quickly and jerk-free. The same is true for other transient operating conditions, such as a sudden change into overdrive or return from overdrive. Any delays, irregularities or variations in vehicle response as a result of driver-induced changes are usually felt to be irritating. Examples include fore and aft oscillations (surge), delays in response, oscillations in engine speed or tractive power. Positive feelings are evoked by prompt accelerator response, smooth engine power, or quiet and stable idling. A vehicle's driveability is significantly influenced by the engine management, but also by engine suspension and design of the power train as a whole. In view of current attempts to optimize fuel consumption and exhaust emissions, maintaining or increasing driveability must be considered as a further target variable.
It is a problem in this context that objective and reproducible criteria in determining a vehicle's driveability are hard to be found in practice, compared with the determination of fuel consumption or exhaust emissions. A further disadvantage is that in the early stages of vehicle development test vehicles are not usually available, so that transient engine management functions must be optimized on a dynamic test stand. Such tests have not been successful so far in producing reliable ratings of a vehicle's driveability.
A conventional test procedure permits driveability assessments when an actual vehicle with defined engine management program is available. It will not be possible in practice, however, to test a multitude of different engine settings in this manner. On the other hand, test bed simulations of a vehicle's power train are not yet refined enough to yield reliable driveability ratings.
For these reasons driveability ratings have so far been made during the later stages of vehicle development, based on subjective assessments of experienced test drivers. With the use of time-consuming test routines a sequence of driveability-relevant maneuvres are performed; vehicle behaviour is rated on answer sheets. Due to the subjective character of such ratings their reproducibility is only limited, however.